Stay Cable for Structures

ABSTRACT

A mast is erected to support a load. At least one stay cable supports the mast. The stay cable is oriented to the mast within a radial distance of the blade from the mast. The stay cable is stressed to support the mast while the wind drives the blade without collision of the stay cable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/181,551, filed Jul. 13, 2011, and now issued as U.S. Pat. No. ______,and incorporated herein by reference in its entirety. This applicationalso relates to U.S. application Ser. No. 13/084,693, filed Apr. 12,2011, entitled “Parallel Wire Cable,” and incorporated herein byreference in its entirety.

COPYRIGHT NOTIFICATION

A portion of the disclosure of this patent document and its attachmentscontain material which is subject to copyright protection. The copyrightowner has no objection to the reproduction by anyone of the patentdocument or the patent disclosure, as it appears in the United StatesPatent and Trademark Office patent files or records, but otherwisereserves all copyrights whatsoever.

BACKGROUND

Exemplary embodiments generally relate to development of renewableenergy resources and, in particular, to the development of renewablewind energy. Exemplary embodiments generally relate to structures thatsupport wind turbines or antennas, to dynamo plants, and to fluidreaction surfaces (i.e., impellers) and, more particularly, tostructures with bracing or guys.

High oil prices have renewed our interest in wind energy. Wind turbinesare being planned and built to convert wind energy into electricity.Some wind turbines are built atop masts, while other wind turbines aresupported by towers. A mast is a vertical structure supported by one ormore stay cables (or “guys”). The stay cables provide stability to themast to reduce oscillations from wind and seismic events. A tower, onthe other hand, is a larger, stronger, and more expensiveself-supporting structure designed to withstand the wind and seismicevents. While the mast is less expensive than the self-supporting tower,additional land is needed for the stay cables. Moreover, the mast mustwithstand a sizable portion of the wind and seismic events. Often, then,design tradeoffs are required when stay cables are used.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The features, aspects, and advantages of the exemplary embodiments arebetter understood when the following Detailed Description is read withreference to the accompanying drawings, wherein:

FIG. 1 is a schematic illustrating an operating environment, accordingto exemplary embodiments;

FIGS. 2 and 3 are schematics illustrating a wind energy installation,according to exemplary embodiments;

FIGS. 4 and 5 are schematics illustrating free body diagrams formonopole designs, according to exemplary embodiments;

FIG. 6 is another schematic illustrating the wind energy installation,according to exemplary embodiments;

FIG. 7 is a detailed schematic illustrating a maximum orientation of astay cable, according to exemplary embodiments;

FIG. 8 is another more detailed schematic illustrating the wind energyinstallation, according to exemplary embodiments; and

FIG. 9 is a schematic illustrating an antenna installation, according toexemplary embodiments.

DETAILED DESCRIPTION

The exemplary embodiments will now be described more fully hereinafterwith reference to the accompanying drawings. The exemplary embodimentsmay, however, be embodied in many different forms and should not beconstrued as limited to the embodiments set forth herein. Theseembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the exemplary embodiments to those ofordinary skill in the art. Moreover, all statements herein recitingembodiments, as well as specific examples thereof, are intended toencompass both structural and functional equivalents thereof.Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture (i.e., any elements developed that perform the same function,regardless of structure).

Thus, for example, it will be appreciated by those of ordinary skill inthe art that the diagrams, schematics, illustrations, and the likerepresent conceptual views or processes illustrating the exemplaryembodiments. Those of ordinary skill in the art further understand thatthe exemplary cables described herein are for illustrative purposes and,thus, are not intended to be limited to any particular manufacturingprocess and/or manufacturer.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless expressly stated otherwise. Itwill be further understood that the terms “includes,” “comprises,”“including,” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. It will be understood thatwhen an element is referred to as being “connected” or “coupled” toanother element, it can be directly connected or coupled to the otherelement or intervening elements may be present. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

It will also be understood that, although the terms first, second, etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another.

Exemplary embodiments conserve energy and further develop renewableenergy sources. Exemplary embodiments describe a superior stay cable forvertical and non-vertical structures, such as monopoles, wind turbines,antennas, and buildings. The stay cable of this invention is constructedusing parallel wires, whereas conventional stay cables are wound strandsof wires. The parallel wire construction has superior strength andstiffness when compared to conventional strand cable. Moreover,exemplary embodiments have a much smaller diameter and weigh less thanconventional strand cable. Exemplary embodiments thus describe asuperior stay cable that reduces the costs of monopoles, wind turbines,antennas, and buildings.

Because the stay cable is stronger than conventional designs, thestructures may be reduced in size and/or weight. Wind turbines,antennas, and any other generally vertical structure may thus be cheaperto manufacture, cheaper to transport, and cheaper to build. Masts thatsupport wind turbines, for example, may be smaller, lighter, andcheaper, thus improving a cost-benefit analysis of alternative windenergy. Less material and labor are required to manufacture and erectwind turbines. Smaller and lighter designs also reduce transportationcosts. Exemplary embodiments thus reduce the costs of alternative windenergy and reduce reliance on fossil fuel.

FIG. 1 is a schematic illustrating an operating environment, accordingto exemplary embodiments. FIG. 1 illustrates a generally verticalstructure 20 supported by at least one stay cable 22. The verticalstructure 20 is erected to support any apparatus 24, such as a windturbine, drilling rig, antenna, and/or utility cable (as laterparagraphs will explain). The stay cable 22 may be tensioned to addstability to the vertical structure 20. Because stay cables (or “guys”)have long been used to stabilize structures, this disclosure will notprovide a detailed explanation of known concepts. Here, though, the staycable 22 has superior strength and stiffness when compared toconventional stay cables (as later paragraphs will explain), so the staycable 22 may be orientated at a much smaller angle θ (illustrated asreference numeral 26) than conventional designs. Indeed, the improvedstay cable 22 may be oriented at ten degrees (10°) or even less, whereasconventional stay cable designs are traditionally oriented at forty fivedegrees (45°) or more.

FIGS. 2 and 3 are schematics illustrating a wind energy installation 30,according to exemplary embodiments. Here the vertical structure 20 isillustrated as a monopole mast 32 supporting a nacelle 34. The nacelle34 may include an alternator/generator 36 coupled to a rotor assembly38. Wind drives one or more blades 40 of the rotor assembly 38. Therotor assembly 38 turns or drives the alternator/generator 36. Thealternator/generator 36 converts mechanical energy of the rotor assembly38 into electrical energy (either alternating current or direct current,as is known). The wind energy installation 30 is generally well-known tothose of ordinary skill in the art, so this disclosure will not providea detailed explanation of the wind energy installation 30.

The mast 32 is supported by the at least one stay cable 22. Each staycable has an upper end 50 attached to an upper region 52 of the mast 32.Each stay cable 22 also has a lower, opposite end 54 that is anchored tosome point, such as earth 56. The stay cable 22 is tensioned andstressed to stabilize the mast 32. The stay cable 22 may extend anentire length L (illustrated as reference numeral 60) from the upper end50 to the lower, opposite end 54. Dampers or other shock-absorbingdevices may also be used, as is known.

The stay cable 22, though, does not collide with the rotating blade 40.Because the stay cable 22 has superior strength to similarly-sizedconventional designs, the stay cable 22 may be orientated inside thespinning blade 40. Conventional stay cables are traditionally orientedat 45 degrees, so conventional stay cables interfere with a tip 62 ofthe spinning blade 40. The superior stay cable 22 of this invention,though, may be tensioned and still oriented at the much smaller angle θ(illustrated as reference numeral 26) of ten degrees (10°) or even less.That is, as wind spins the blades 40 of the rotor assembly 38, the staycables 22 will not intersect a rotor disk 64 (best illustrated in FIG.3).

FIGS. 4 and 5 are schematics illustrating free body diagrams formonopole designs, according to exemplary embodiments. FIG. 4 illustratescalculations for a height of 270 feet, while FIG. 5 illustratescalculations for a height of 450 feet. These calculations show that thestay cables 22 greatly add stability to the monopole mast 32, even atsmall angles. These calculations also show that the monopole 32 may beincreased in height by using the stronger stay cables 22. Indeed, thebelow calculations show that the monopole mast 32 may be increased inheight (from 270 feet to 450 feet), while maintaining the stay cables 22at less than or equal to seven degrees (7°).

FIG. 4A illustrates a baseline calculation. The mast 32 is assumed to be270 feet in height, ten feet (10′) in diameter, and constructed of steeltube having a one inch (1″) wall thickness. The mast 32 is subjected toa conservative horizontal wind load of 50,000 pounds force (or 50 kips)and a vertical load of 130,000 pounds force (or 130 kips). FIG. 4Aillustrates the mast 32 with no supporting stay cables. Without staycables, the maximum moment at the base is 13,830 kilopounds force feet(or 138.3×10³ feet-pounds force) and a maximum deflection at the tip ofthe mast 32 is 30.4 inches.

FIG. 4B illustrates the braced monopole design. The mast 32 has the samedimensions (e.g., 270 ft. in height, 10 ft. in diameter, and 1″ wallthickness) and loading (50 kips horizontal load and 130 kips verticalload). Here, though, the stay cables 22 brace the mast at ⅓ heights(that is, stay cables 22 are attached at 90 feet, 180 feet, and 270feet). Each stay cable 22 is constructed of steel using parallel wireswith six square inches (6 in²) of total metallic area. Each stay cable22 has a 230 ksi yield stress and a 270 ksi ultimate load capacity. If atop stay cable 22 is oriented at θ=7°, the maximum moment at the base is2,894 kilopounds force feet, and the maximum deflection at the tip ofthe mast 32 is reduced to 6.7 inches. The stresses in the stay cables 22are 172 ksi for the upper stay, 149 ksi for a middle stay, and 81 ksifor a lower stay.

FIG. 4B thus illustrates a substantial improvement. When FIG. 4B iscompared to FIG. 4A, one sees that the stay cables 22 substantiallyreduce deflection at the tip of the mast 32 (6.7 inches verses 30.4inches). Moreover, the stay cables 22 are oriented at seven degrees(7°), which is much less than is used with conventional designs.Conventional stay cables are traditionally oriented at about forty fivedegrees (45°) or more from the mast. Because the stay cables of thisinvention have superior strength, the stay cables may be oriented at themuch smaller angle θ of ten degrees (10°) or even less. Even at suchsmall angles, though, the stresses in the stay cables 22 aresubstantially less than the yield stress, indicating that even smallerangles, smaller diameter cables, and/or higher loads may be used.

Another dramatic comparison is evident. A conventional mast for aconventional wind turbine is fifteen feet (15 ft.) in diameter. Such alarge mast is difficult and costly to transport, often requiringspecialized rail cars and/or barges. The above calculations, though,were based on a mast diameter of only ten feet (10 ft.). Exemplaryembodiments, then, permit the mast 32 to be substantially reduced indiameter, while still supporting equivalent loadings. Moreover, thesmaller mast 32 is more easily transported and may be hauledover-the-road by conventional tractor trailers. The smaller mast 32 alsoweighs substantially less than conventional designs, so material,installation, and erection costs are reduced.

The calculations illustrated by FIGS. 4A and 4B are simple examples. Theabove calculations were based on a mast of ten feet (10′) in diameterand constructed of steel tube having a one inch (1″) wall thickness. Thediameter, wall thickness, and the number of stay cables 22 may varyaccording to the load requirements. Indeed, the mast 32 may be tapered,and the concentric height locations of the stay cables 22 may be variedalong the mast 32 to provide a more efficient design per the individualdesired load required results. The ten feet diameter with one inch (1″)wall thickness thus only illustrates the dramatic reduction in size andcosts that are possible using the stronger stay cables 22.

Exemplary embodiments also reduce other loads. For wind towers, theacute angle θ (illustrated as reference numeral 26) of the stay cables22 may also result in a substantial downward vertical load onconnections between sections of the mast or tower. This vertical load,though, reduces the upward vertical load on the bolted connections fromwind and turbine induced torque, which in turn reduces the tensile andfatigue load on the bolts. The loads used in the above calculations arethe wind shear for the turbine and wind vanes at cut-off wind speed of amaximum 60 miles per hour. These loads reflects data obtained fordeflection at the turbine during power production. For simplicity, fullgravity and maximum code-induced wind loads are not included, but thedesign of the guyed tower will be more than adequate. The turbines arebasically reducing their wind vane connection loads starting at about 35miles per hour until about 60 miles per hour, at which point theturbines may be totally disconnected for any power production.

FIG. 5 illustrates another design comparison. Here the mast is 450 feetin height, but still 10 feet in diameter with a 1-inch wall thickness.The mast 32 is again subjected to the horizontal load of 50,000 poundsforce (or 50 kips) and the vertical load of 130,000 pounds force (or 130kips). FIG. 5A illustrates no supporting stay cables, while FIG. 5Billustrates bracing at ⅓ heights (that is, stay cables 22 are attachedat 150 feet, 300 feet, and 450 feet). Without the stay cables, FIG. 5Aillustrates the maximum moment at the base is 24,106 kilopounds forcefeet with a maximum deflection of 148.3 inches at the tip. In FIG. 5B,though, the mast 32 is again braced by the stay cables 22, with the topstay cable 22 oriented at seven degrees (7°). The maximum moment at thebase is 3,400 kilopounds force feet, and the maximum deflection at thetip of the mast is reduced to 14.9 inches. The stresses in the staycables are 235 ksi for the upper stay, 149 ksi for a middle stay, and 81ksi for a lower stay.

Again, then, the stay cables 22 provide substantial improvements. Evenwhen the mast 32 is increased in height to 450 feet, the orientation ofseven degrees (7°) still maintains deflection to less than fifteeninches. Even at this higher height, the stresses in the stay cables 22are still within acceptable safety limits. The diameter of the mast 32is still substantially smaller than conventional designs (10 feet verses15 feet), so the mast 32 weighs less, is easier to transport, and iseasier to erect. Exemplary embodiments thus provide substantiallyreduced costs for wind turbines, drilling rigs, antennas, and any othervertical mast.

FIG. 6 is another schematic illustrating the wind energy installation30, according to exemplary embodiments. Because the stay cable 22 hassuperior strength, the stay cable 22 may be attached at a higher height,and anchored at a lesser distance from the mast 32, than traditionaldesigns. Indeed, exemplary embodiments may be oriented above the tip 62of the blade 40 without collision. As FIG. 6 illustrates, the upper end50 of the stay cable 22 is attached at a height 70 greater than the tip62 of the blade 40 of the rotor assembly 38. The upper end 50 of thestay cable 22 is attached near or at a top 72 of the mast 32. The lower,opposite end 54 of the stay cable 22 is anchored at a distance D_(B)(illustrated as reference numeral 74) from a base 76 of the mast 32. Thestay cable 22 is strong enough to wholly extend the entire length L(illustrated as reference numeral 60) from the upper end 50 to thelower, opposite end 54. The stay cable 22 may even comprise multiple,spliced sections or elements to extend the length L (or longer). Dampersor other shock-absorbing devices may also be used, as is known.

The angle θ may be mathematically defined. The mast 32 has a heightH_(M) (illustrated as reference numeral 80), and the upper end 50 of thestay cable 22 is attached at a height H_(S) (illustrated as referencenumeral 82). The lower, opposite end 54 of the stay cable 22 is anchoredat the distance D_(B) (illustrated as reference numeral 74) from thebase 76 of the mast 32. The stay cable 22 is attached at the muchsmaller acute angle θ (illustrated as reference numeral 26) thanconventional designs. The acute angle θ may be determined from thetrigonometric relation:

${\tan \; \theta} = \frac{D_{B}}{H_{S}}$

For maximum support, though, the stay cable 22 may be attached as highup the mast 32 as needed. The stay cable 22 is strong enough to beattached at or nearly equal to the height H_(M) of the mast 32.Substitution yields:

${\tan \; \theta} = \frac{D_{B}}{H_{M}}$

As the above paragraphs explained, the angle θ is substantially lessthan conventional designs. The angle θ, in fact, may be in the range ofnearly zero to ten degrees (0>θ≧10), which is much less than thatpossible with conventional designs. Indeed, as the calculationsaccompanying FIGS. 4 and 5 showed, the angle θ may be about sevendegrees (7°) for common wind turbine loading.

FIG. 7 is a detailed schematic illustrating a maximum orientation of thestay cable 22, according to exemplary embodiments. For simplicity,though, the mast 32 is only partially illustrated. As earlier paragraphsexplained, the rotating blade 40 cannot collide with the stay cable 22.The stay cable 22, when tensioned and stressed, cannot impinge orintersect the spinning blade 40 (e.g., the rotor disk 64 illustrated inFIG. 3). As FIG. 7 illustrates, then, the angle θ has a maximum valueθ_(max) that permits unobstructed rotation of the rotor assembly 38. Ifthe orientation of the stay cable 22 exceeds the angle θ_(max), then therotating blade 40 may impact the stay cable 22. The angle θ_(max) maythus be expressed in terms of a distance D_(Tip) (illustrated asreference numeral 90) between the mast 32 and a width of the tip 62 ofblade 40. (The distance D_(Tip) is affected by the mounting and/orgearing of the nacelle 34, the design of the blade 40, and otherconsiderations which are not relevant here.) FIG. 7 illustrates asituation when the tip 62 of the blade 40 is in its lowest position(e.g., a six o'clock position), and the distance D_(Tip) is measuredradially and normally from an outer surface 92 of the mast 32. Themaximum value of the acute angle θ is calculated as:

${{\tan \; \theta_{m\; {ax}}} = \frac{D_{Tip}}{\left( {H_{S} - H_{B}} \right)}},$

where H_(B) (illustrated as reference numeral 94) is a height of the tip62 of the blade 40 of the rotor assembly 38, as measured from earth orground 56. As the wind energy installation 30 is being designed, themaximum angular orientation of the stay cable 22 (e.g., the maximumvalue of the angle θ_(max)) may be determined from the height of themast 32, the height of the tip 62, and the distance D_(Tip). Anyorientation greater than θ_(Max) may cause the stay cable 22 to collidewith the rotating blade 40. Because conventional stay cables must bemuch larger in diameter, the larger diameter prohibitively increasescosts and is too heavy to handle.

Exemplary embodiments thus reduce the costs of the wind energyinstallation 30. Because the stay cable 22 is superior to conventionaldesigns, the stay cable 22 may be attached higher up the mast 32 (e.g.,the height H_(S)), and closer to the base 68 (e.g., the distance D_(B)).Moreover, the size of the mast 32 may be reduced for a given weight ofthe nacelle 34. Conversely, the mast 32 may support a greater size andweight of the nacelle 34, thus allowing the rotor assembly 38 and thealternator/generator 36 to be increased in capacity to generate moreelectricity. For example, longer blades may be used to turn a largeralternator/generator 36. Regardless, material, transportation, and laborcosts are reduced for a given design of the wind energy installation 30.

FIG. 8 is another more detailed schematic illustrating the wind energyinstallation 30, according to exemplary embodiments. Here the blade 40of the rotor assembly 38 may deflect due to wind. As wind encounters theblade 40, forces against the blade 40 may cause the blade 40 to bend ordeflect. As FIG. 8 illustrates, the wind may deflect the tip 62 of theblade 40 a deflection distance D_(def) (illustrated as reference numeral94). The deflection distance D_(def) will depend on the design, size,and material of the blade 40, along with wind speed, and perhaps evenother factors. Regardless, any deflection in the blade 40 will reducethe distance D_(Tip) (illustrated as reference numeral 90) between themast 32 and the tip 62 of blade 40. The maximum value of the acute angleθ may thus be modified to account for the deflection distance D_(def) ofthe blade 40:

${\tan \; \theta_{{Ma}\; x}} = {\frac{\left( {D_{Tip} - D_{def}} \right)}{\left( {H_{S} - H_{B}} \right)}.}$

If the blade 40 deflects due to wind forces, then the maximum acuteangle θ_(Max) of the stay cable 22 may be computed to still preventcollisions with the rotating, deflecting blade 40.

The above calculations apply to swiveling nacelles. Some nacelles aremounted to a bearing which permits the nacelle 34 to turn, or swivel,about the mast 32. The nacelle 34 may thus capture wind energy from anydirection, still without collision of the stay cable 22. Because thenacelle 34 may swivel about a centerline of the mast 32, each stay cable22 must have an orientation that clears the rotor disk 64 (illustratedin FIG. 3) in any direction of wind. As the nacelle 34 swivels about avertical axis of the mast 32, the tip 62 of the blade 40 traces a circleabout the mast 32. The circle has a radius R_(Tip) that is equal to thedistance D_(Tip) (illustrated as reference numeral 90 in FIGS. 7 & 8)between the mast 32 and the tip 62 of blade 40. That is, when thenacelle 34 swivels about the mast 32, the tip 62 of the blade 40 definesa zone beyond which any stay cable 22 cannot be placed. If the staycable 22 is oriented outside the circle (of radius D_(Tip)) at theheight H_(B) (illustrated as reference numeral 94), then the stay cable22 may collide with the spinning blade 40. Again, then, the maximumvalue of the angle θ is calculated as:

${{\tan \; \theta_{M\; {ax}}} = \frac{D_{Tip}}{\left( {H_{S} - H_{B}} \right)}},$

where H_(B) is the height of the tip 62 of the blade 40 of the rotorassembly 38, as measured from earth or ground. The acute angle θ mayalso be corrected for wind deflection of the blade 40 (as explainedabove), thus yielding:

${\tan \; \theta_{{Ma}\; x}} = {\frac{\left( {D_{Tip} - D_{Def}} \right)}{\left( {H_{S} - H_{B}} \right)}.}$

At the height H_(B) of the tip 62 of the blade 40, the orientation ofthe stay cable 22 may not exceed the maximum acute angle θ_(Max) and/orthe distance (D_(Tip)−D_(Def)). Prudent designers may even include asafety factor that further reduces θ_(Max).

The above figures illustrate that the vertical structure 20 (e.g., themast 32) may have any number of the stay cables 22. If the verticalstructure 20 is a utility pole, for example, then perhaps only a singlestay cable 22 is needed. Other vertical structures, however, may requiretwo, three, or more stay cables (as FIGS. 4 and 5 illustrated). Multiplestay cables 22 may be radially configured about the mast 32 in equally-or unequally-spaced arrangements.

The mast 32 may have any design and/or construction. The mast 32 may beconstructed of any material, such as steel, aluminum, composite,concrete, and/or wood. The mast 32 may have a tubular, tapered, conical,and/or lattice design. The mast 32 may also have any height; indeed,many of the world's tallest structures are radio masts that supportcommunications equipment. The mast 32, though, may support any equipmentor load, including oil rigs or platforms, electrical equipment, bridges,and observation decks.

FIG. 9 is a schematic illustrating an antenna installation 100,according to exemplary embodiments. Here the mast 32 is erected tosupport communications equipment 102, such as an antenna 104 for radioand/or cellular networks. The upper end 50 of the stay cable 22 attachesto or near the top 72 of the mast 32, while the lower, opposite end 54anchors at the earth or ground 56. Again, the stay cable 22 is stressedto support the mast 32 at the acute angle θ (illustrated as referencenumeral 26). Because the stay cables 22 have superior strength forsimilar sizes of conventional strand designs, the stay cables 22 may beoriented such that the angle 26 is less than or equal to ten degrees(10°).

The stay cables 22 may include other features. Tall masts, for example,may reach into controlled airspace, so the mast 32 and/or the staycables 22 may require lights, visible flags, or other safety markers.When the stay cables 22 are used with the communications equipment 102,any insulator may sheath at least a portion of the stay cable 22 toimprove electromagnetic properties (e.g., insulation or conductivity).

The stay cables 22 may also include any end attachments. The upper end50 of the stay cable 22, for example, may utilize any means of attachingthe stay cable 22 to the mast 32. The opposite, lower end 54 may,likewise, utilize any means of anchoring to the ground or earth.

The stay cables 22 may also be utilized in any environment. Many windturbines, oil platforms, antennas, and other vertical structures areerected in the ocean. Other vertical structures are erected onshore.Exemplary embodiments may be utilized in any onshore or offshoreinstallation and in any ambient environment (e.g., mountains, deserts,arctic poles, plains, beaches).

The stay cables 22 may also support cantilevered structures. Somestructures outwardly cantilever, such as entry overhangs, pedestrianoverlooks, and even portions of buildings (e.g., the ClintonPresidential Library and Museum in Little Rock, Arkansas USA). The staycables 22 may be used to support cantilevered structures at the acuteangle θ (illustrated as reference numeral 26) without obtrusive bracing.The strength of the stay cables 22 may thus be advantageously used inthe design of cantilevered structures.

The stay cables 22 have a parallel construction. Each individual wire inthe stay cable 22 is parallel to every other wire. The individual wiresin the stay cable 22 are parallel along their entire length and may alsobe equal in length to every other wire. Each wire in the stay cable 22is also individually pretensioned. Exemplary embodiments apply a tensionvalue to each wire in the stay cable 22. That is, each individual wirein the stay cable 22 may have an equal, or nearly equal, tension toevery other wire in the stay cable 22. Exemplary embodiments pretensionevery wire in the stay cable 22. The tension value is individuallyapplied or pulled to each wire in the stay cable 22. Individualpre-tensioning of each wire provides lighter, cheaper, and stronger staycable designs. An individually-tensioned stay cable 22 weighssignificantly less than conventional designs, but the strength of thestay cable 22 is still greater than conventional designs. Alternatively,exemplary embodiments may be used to construct a stay cable 22 that issimilar in size to conventional designs, but is substantially strongerto support greater loads. Regardless, exemplary embodiments offergreater design alternatives that require less material cost. If thereader desires a more detailed explanation, the reader is invited toconsult U.S. application Ser. No. 13/084,693, filed Apr. 12, 2011,entitled “Parallel Wire Cable,” and incorporated herein by reference inits entirety.

Tension is applied to each wire, not strands of wires. Methods are knownthat tension strands of plural wires. A strand, in the art of staycable, is defined as a group of multiple wires. Conventional methods areknown that apply tension to a strand of multiple wires. Exemplaryembodiments, in contradistinction, apply the tension value to eachindividual wire in the stay cable 22. Each wire has the equal tensionvalue as every other wire in the stay cable 22.

While the exemplary embodiments have been described with respect tovarious features, aspects, and embodiments, those skilled and unskilledin the art will recognize the exemplary embodiments are not so limited.Other variations, modifications, and alternative embodiments may be madewithout departing from the spirit and scope of the exemplaryembodiments.

What is claimed is:
 1. A apparatus, comprising: a mast; a rotor assemblysupported by the mast, the rotor assembly having a blade driven by wind;and a stay cable supporting the mast, the stay cable oriented to themast within a radial distance of the blade from the mast, the stay cablestressed to support the mast while the wind drives the blade withoutcollision of the stay cable.
 2. The apparatus according to claim 1,wherein the stay cable is oriented at an angle not exceeding ten degreesfrom the mast.
 3. The apparatus according to claim 1, wherein the staycable is oriented at an angle not exceeding seven degrees from the mast.4. The apparatus according to claim 1, wherein the stay cable has an endattached near an upper end of the mast.
 5. The apparatus according toclaim 1, wherein the stay cable has an end anchored at earth.
 6. Theapparatus according to claim 1, further comprising a generatorconverting mechanical energy of the rotor assembly into electricalenergy.
 7. The apparatus according to claim 1, further comprising analternator converting mechanical energy of the rotor assembly intoelectrical energy.
 8. The apparatus according to claim 1, wherein thestay cable is oriented inside a rotor disk of the rotor assembly.
 9. Theapparatus according to claim 1, wherein the rotor assembly swivels tocapture the wind from any direction.
 10. A method, comprising:supporting a rotor assembly by a mast; attaching an end of a stay cableto an attachment at an upper region of the mast; anchoring an oppositeend of the stay cable; orienting the stay cable to the mast within aradial distance of the blade from the mast; and tensioning the staycable to a stressed condition to support the mast while wind rotates theblade without collision of the stay cable.
 11. The method according toclaim 10, further comprising orienting the stay cable at an angle to themast not exceeding seven degrees.
 12. The method according to claim 10,further comprising orienting the stay cable at an angle to the mast notexceeding ten degrees.
 13. The method according to claim 10, furthercomprising converting mechanical energy of the rotor assembly intoelectrical energy.
 14. The method according to claim 10, furthercomprising converting rotational energy of the rotor assembly intoelectrical energy.
 15. The method according to claim 10, furthercomprising orienting the stay cable inside a rotor disk of the rotorassembly.
 16. The method according to claim 10, further comprisingorienting the stay cable according to a height of a tip of the blade.17. The method according to claim 10, further comprising swiveling therotor assembly to capture the wind from any direction.
 18. The methodaccording to claim 10, further comprising orienting the stay cableaccording to a trigonometric relation tan$\theta = {\frac{D_{B}}{H_{S\;}}.}$
 19. The method according to claim10, further comprising orienting the stay cable according to atrigonometric relation tan $\theta = {\frac{D_{B}}{H_{M}}.}$
 20. Themethod according to claim 10, further comprising orienting the staycable according to a trigonometric relation tan$\theta_{m\; a\; x} = {\frac{D_{Tip}}{\left( {H_{S} - H_{B}} \right)}.}$